Not sure tbh, I went through with my two xSeries in 1 session, and I know what I’m getting myself into. It seems to be my bodies response to them (or my unconscious thoughts), plus maybe some anxiety? I wouldn’t say extreme fear though 
Maybe it is and just the adrenaline rush clouded / overwhelmed that feeling 
Regardless, I’m gonna get more implants, and hopefully my Titan sometime. I’m hoping people try a needle installation too (maybe palm side P0?)